It is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) or outside (outboard) the hull. The drive shaft of the water jet apparatus is coupled to the output shaft of the motor. The impeller is mounted on the drive shaft and installed in a housing, the interior surface of which defines a water tunnel having a convergent nozzle. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the water tunnel and out the convergent nozzle. The reaction force propels the boat forward.
In many water jet apparatus designs, the flow-through housing comprises an outer tubular section and a central hub, the outer tubular section and central hub being generally concentrically arranged to define a generally annular passageway downstream of the impeller. This passageway forms part of the water tunnel. The outer tubular section is sometimes referred to as the "stator housing" while the central hub is called the "stator hub". The stator hub typically rotatably supports the impeller shaft. The stator hub is supported inside the stator housing by a plurality of stator vanes or ribs which are curved to straighten the swirling water flowing downstream from the impeller. This straightening of the impelled water absorbs energy, resulting in a loss of efficiency of the water jet propulsion unit or pump. There is a need for a mechanism which would decrease the amount of energy lost due to flow straightening by the stator vanes.